Malnutrition in children with cystic fibrosis (CF), results from a complex interaction of chronic pulmonary disease, increased energy expenditure, malabsorption, and recurrent infection. Growth-stimulating peptides promote anabolism in nutritionally compromised patients. Our goal is to test the following hypothesis: Treatment with insulin-like growth factor-I (IGF-1), which subserves the anabolic properties of growth hormone, will result in enhanced linear growth, increased lean body mass and improved lung function in nutritionally compromised children with CF.